<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  .div1{
    width: 100px;
    height: 100px;
    background-color: red;

  }
</style>
<body>
  <div class="div1">加了div标签</div>
  <button class="btn">我是按钮</button>
  <p>今天天气不错</p>
</body>
</html>